Malaria, the mosquito-borne disease blamed for the deaths of more than 1 million young children every year, is expected to become more pronounced under climate change. Credit: Jez via flickr

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The World Health Organization predicts that an additional 250,000 people will die annually between 2030 and 2050 from conditions caused or exacerbated by climate change, the Geneva-based agency reported yesterday in an update of climate mortality estimates.

But the causes of sickness and death will shift over that period as child deaths from malnutrition and diarrheal disease decline across much of the world, while mortality rises from things like mosquito-borne malaria, heat exposure and other conditions, especially in South Asia and sub-Saharan Africa.

"Overall, climate change is projected to have substantial adverse impacts on future mortality, even considering only a subset of the expected health effects," the agency said in its latest "Quantitative Risk Assessment of the Effects of Climate Change on Selected Causes of Death." And those impacts are expected to be felt even "even under optimistic scenarios of future socioeconomic development."

At the same time, the agency said, adverse health effects from climate change "will be distributed unequally within and between populations," with wealthier countries and regions generally being better able to adapt to and mitigate against the harshest effects.

According to WHO, deaths from heat exposure will be especially pronounced over the coming decades, from 92,000 to as much as 250,000 deaths worldwide per year by midcentury, with the greatest rates of death occurring in the world's poorest regions.

Wealthy nations not spared
But the developed world won't be spared from the effects of rising temperatures, according to WHO.

"An increase in acute mortality associated with high temperatures has been observed in nearly all populations where it has been studied," the authors state. And while human populations are largely adapted to local climates, researchers point to "an increase in mortality risk observed at both high and low temperatures in populations in temperate and cold climates ... and tropical and subtropical areas."

For example, nearly 3,000 heat-related deaths are expected annually among elderly populations in the United States and Canada by 2030, even with modest adaptation levels. Europe, meanwhile, could see 5,500 heat-related mortalities each year through 2020.

By 2050, North American and European annual heat deaths should rise to roughly 6,100 and 10,500, respectively, even with modest adaptation. Under a no-adaptation scenario, the projected mortalities for North America and Europe shot to 16,000 and 27,300, respectively.

Emails to officials at WHO were not returned yesterday afternoon.

Jeremy Hess, an Emory University physician and epidemiologist who has studied the relationship between climate change and health conditions, said in an email that the WHO findings are "a significant step forward in the global estimation of projected disease burden associated with climate change." But he also cautioned that the morbidity estimates "are almost certainly an underestimate" because a number of climate-health relationships are not measurable due to lack of adequate data.

Gary Cohen, president and founder of the Massachusetts-based nonprofit Health Care Without Harm, said in a telephone interview that the risks of climate change to both the health of U.S. citizens and the U.S. health care delivery system is profound, particularly in urban areas, where warming average temperatures are exacerbated by the heat island effect and high concentrations of other air pollution like ozone and particulate matter.

"For vulnerable populations like the elderly and shut-ins, just getting people into cooler, cleaner air could be the difference between life and death," he said.

Yet many U.S. hospitals lack the very equipment and protocols that can make their buildings, staff and patients more climate-resilient, especially during extreme events that disrupt grid-delivered power supplies. "When the grid is down, a lot of hospitals can't deliver basic services, so that becomes another liability," Cohen said.

Coastal flooding could add deaths
In the world's poor and developing regions, malaria and diarrheal diseases related to water shortages and water contamination will claim in excess of 100,000 lives by 2030, according to the WHO analysis.

Malaria, the mosquito-borne disease blamed for the deaths of more than 1 million young children every year, is expected to become more pronounced under climate change, "in part because higher ambient temperatures increase the metabolic rate of [malaria-carrying mosquitoes], thereby leading to more frequent blood meals," the report said.

"In addition, higher temperatures support faster development of the malaria parasite within the mosquito, increasing the probability that vectors will become infective before they die." Malaria is also affected by shifts in seasonal rainfall and humidity, as well as land-use change and urbanization.

The analysis, which relies on five models of climate change and health outcomes, advances earlier studies done in 2004 and 2006, but "it is still constrained by limited quantitative information about, and understanding of, causal mechanisms linking climate with health impacts on a global and local scale," the authors said.

Also, the new mortality estimates, while dramatically higher than the approximately 150,000 annual deaths attributed to climate change stress in WHO's last assessment in 2004, are not directly comparable to earlier studies, which relied on different models and different underlying scenarios.

The latest assessment also did not account for the effects of extreme weather except for coastal flooding due to sea-level rise and storm surge. This is largely because "extreme events are not well described by climate data averaged over space and time," the authors said.

"Climate change may increase the burden of mortality from coastal flooding, but the impacts are highly uncertain and depend crucially on adequate coastal defenses and disaster preparedness," the report adds.

While the focus of the WHO's findings is on health risks and associated morbidity, the authors noted that climate change will have some positive, although limited, effects on human health. For example, "There are likely to be reductions in cold-related mortality and morbidity in high-income populations," the report found.

Also, climate change may allow some tropical and subtropical crops to thrive at mid-latitudes where they previously did not grow, but such changes could also improve conditions for crop pests and the spread of plant and animal diseases.

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